The conventional art of this kind includes one disclosed in JP-A-2003-157122. The conventional joystick disclosed in this JP-A-2003-157122 has a control member, specifically a control lever, a rocking means and a rotary potentiometer. The control lever is pivotally controlled by an operator in a predetermined direction or a direction opposite to the predetermined direction. The rocking means comprises gymbals and a cam, which are rockable as a result of a pivotal movement of the control lever. The rotary potentiometer has a support pin with the rocking means supported thereon and a rotary shaft rotatable as a result of a rocking motion of the rocking means, and outputs a rotation angle signal responsive to rotation of the rotary shaft.
The conventional joystick disclosed in JP-A-2003-157122 is also provided with an extension arm, a pivotable arm, and a linkage. The extension arm is arranged integrally on a support pin, and extends toward the rotary potentiometer. The pivotable arm is connected to the extension arm pivotably within a vertical plane parallel to a plane in which a range of pivotal movements of the extension arm is included, and is arranged integrally on the rotary shaft of the rotary potentiometer. The linkage connects the pivotable arm and the extension arm together with predetermined clearances interposed therebetween in the predetermined direction and opposite direction in which the control member is controlled.
The conventional joystick disclosed in JP-A-2003-157122 is further provided with a torsion coil spring, an expanding means, specifically a stopper in the form of a short pin, and a holding pin. The torsion coil spring normally holds the pivotable arm of the rotary potentiometer in a neutral position. The stopper is arranged on the pivotable arm, and upon pivotal movement of the pivotable arm, causes the torsion coil spring to expand. The holding pin is arranged on a housing main body of the rotary potentiometer, and holds the torsion coil spring at its coil portion.
In the conventional joystick of JP-A-2003-157122 constructed as described above, pivotal control of the control level, for example, in the predetermined direction causes the extension arm to pivot about the support pin, and as a result, the pivotable arm pivots via the linkage. Accordingly, the rotary shaft of the rotary potentiometer, said rotary shaft being arranged integrally on the pivotable arm, rotates so that a rotation angle signal corresponding to the stroke of the control lever is outputted. Responsive to the rotation angle signal, an actuator such as an arm cylinder arranged on a hydraulic excavator is driven.
With reference to FIGS. 12A and 12B, a description will now be made about a correlation between the coil portion of the above-mentioned torsion coil spring and the holding pin arranged on the rotary potentiometer and holding the torsion coil spring thereon, although such a correlation is not described specifically in JP-A-2003-157122 referred to in the above.
FIGS. 12A and 12B shows a holding pin 30 arranged on the rotary potentiometer, a torsion coil spring 21 held at a coil portion 21c thereof on the holding pin 30, a rotary shaft 13 of the rotary potentiometer, a stopper 18 arranged on the rotary potentiometer and capable of being brought into contact with arm portions 21a, 21b arranged in continuation with the coil portion 21c of the torsion coil spring 21, and an expanding means, specifically a pin 19 formed on an unillustrated pivotable arm, which is arranged integrally with the rotary shaft, and capable of causing the torsion coil spring 12 to expand. The pin 19 corresponds to the stopper in the form of a short pin, which constitutes the expanding means disclosed in JP-A-2003-157122.
FIG. 12A illustrates the form of the torsion coil spring 21 when the control lever is held in its neutral position. The diameter A of the stopper 18 and the diameter B of the pin 19 are set at the same dimension and, when the torsion coil spring 21 is in the neutral position illustrated in FIG. 12A, the arm portions 21a, 21b of the torsion coil spring 21 are in contact with the stopper pints 18 and 19, respectively, so that the distance L between these arms 21a and 21b becomes the same as the diameter A of the stopper 18 and the diameter B of the pin 19.
Now assume that the torsion coil spring 21 is in the neutral position as described above and the diameter C of the holding pin 30 is set equal to the inner diameter of the coil portion 21c of the torsion coil spring 21. When the torsion coil spring 21, for example, its arm 21a is caused to expand by a movement of the pin 19 as a result of a pivotal movement of the pivotable arm as illustrated in FIG. 12B, the coil portion 21c of the torsion coil spring 21 contracts in such a way that its diameter becomes smaller. As a result, the coil portion 21c progressively cinches up the holding pin 30, and therefore, an excessive tensile force acts on the coil portion 21c, leading to a potential problem that the coil portion 21 may be broken.
For the reasons mentioned above, the diameter of the holding pin 30 that holds the torsion coil spring 21 is generally set substantially smaller than the inner diameter of the coil portion 21c of the torsion coil spring 21 at the time that the torsion coil spring 21 is in its neutral position.
Because the diameter of the holding pin 30 with the torsion coil spring 21 held thereon is set smaller as mentioned above than the inner diameter of the torsion coil spring 21 at the time that the torsion coil spring 21 is in its neutral position, the conventional joystick is accompanied with inconveniences. A description will hereinafter be made about these inconveniences.
FIGS. 13A through 13C illustrate the construction of an essential part of the rotary potentiometer provided in the conventional art, FIG. 13A is a front view, FIG. 13B is a view corresponding to an H1 section of FIG. 13A, and FIG. 13C is a view corresponding to an H2 section of FIG. 13B. FIGS. 14A and 14B illustrate the inconveniences which arise with the conventional joystick, FIG. 14A shows the inconvenience which arises when the control lever has been controlled in the predetermined direction, and FIG. 14B depicts the inconvenience which arises when the control lever has been controlled in the opposite direction. FIG. 15 diagrammatically shows output characteristics of the rotational potentiometer in the conventional joystick.
FIGS. 13A through 13C illustrate states when the diameter D of a holding pin 20 arranged on a rotary potentiometer 11 is set smaller than the inner diameter of a coil portion 21c of a torsion coil spring 21. Also illustrated is a pivotable arm 14 arranged integrally on a rotary shaft 13 of the rotary potentiometer 11. In this pivotable arm 14, a slot 15 that constitutes a linkage is formed. FIG. 13(B) depicts a cover member 31, which limits movements of the rotary shaft 13 along an axis thereof, and a screw 23 maintained in threaded engagement with a threaded portion formed on the holding pin 20. The remaining elements are the corresponding elements in the above-described FIGS. 12A and 12B.
In such conventional art as described above, when an unillustrated control lever is pivotally controlled in a predetermined direction, for example, toward the viewer from the neutral position shown in FIGS. 13A and 13B, the pivotable arm 14 of the rotary potentiometer 11 pivots as a result of the pivotal movement of the control lever as illustrated in FIG. 13C. At this time, force F is applied to the arm portion 21a of the torsion coil spring 21 via a pin 19 of the pivotable arm 14, and therefore, the torsion coil spring 21 moves until the coil portion 21c is brought into contact with the holding pin 20.
When the unillustrated lever is controlled back from such a controlled position to its neutral position, the torsion coil spring 21 may incline beyond a position which the torsion coil spring 21 is supposed to assume when it is in the original neutral position, that is, the position illustrated in FIG. 13A. As a result, a problem arises in that as shown in FIG. 14A, the pivotable arm 14 stops at a position nearer by an angle η than the original neutral position to which the pivotable arm 14 is supposed to return.
Designated at numeral 16 in FIGS. 14A and 14b is a protuberance formed on an unillustrated extension arm which pivots as a result of control of the control lever. By this protuberance 16 and the slot 15 of the pivotable arm 14, a linkage is constructed such that the pivotable arm 14 and the unillustrated extension arm are connected together with predetermined clearances interposed therebetween in the predetermined direction and the opposite direction.
If the pivotable arm 14 of the rotary potentiometer 11 fails to fully return to the neutral position by the angle η despite the return of the control lever to the neutral position as mentioned above, a voltage is outputted as an output error ΔV from the rotary potentiometer 11 as shown in FIG. 15 although the output voltage is supposed to be 0 V.
A similar situation takes place when the unillustrated lever is pivotally controlled in the direction opposite to the above-mentioned pivotal control in the predetermined direction. As illustrated in FIG. 14B, the coil portion 21c of the torsion coil spring 21 still remains in contact with the holding pin 20 despite the control of the control lever back to the neutral position. This results in a situation that the pivotable arm 14 fails by an angle η to fully return to the neutral position to which the pivotable arm 14 is supposed to return.
Described specifically, in the prior art including the joystick disclosed in JP-A-2003-157122, the coil portion 21c of the torsion coil spring 21, as a result of a pivotal movement of the pivotable arm 14 of the rotary potentiometer 11, is allowed to move until it comes into contact with the holding pin 20. As a consequence, upon controlling back the control lever to the neutral position, a displacement takes place relative to the original neutral position to which the pivotable arm 14 is supposed to return, thereby developing a problem that deteriorations take place in output characteristics.
FIGS. 16, 17A and 17B illustrate other inconveniences of the conventional art. FIG. 16 shows a state at the time of control, while FIGS. 17A and 17B depicts states at the times of returns to the neutral position, respectively. Described specifically, FIG. 17A illustrates an inconvenience that takes place when the control lever is controlled in the predetermined direction, and FIG. 17B depicts another inconvenience that takes place when the control lever is controlled in the direction opposite to the predetermined direction.
FIG. 16 illustrates around the rotary potentiometer, and as mentioned above, shows the holding pin 20 arranged on the housing main body of the rotary potentiometer 11, the torsion coil spring 21 held at its coil portion 21c by the holding pin 20, the rotary shaft 13 of the rotary potentiometer 11, a stopper 18 arranged on the housing main body of the rotary potentiometer 11 to limit movements of the arm portions 21a, 21b of the torsion coil spring in the neutral position, and an expanding means, specifically a pin 19 which is formed on the above-mentioned pivotable arm 14 arranged integrally with the rotary shaft 13 and causes the torsion coil spring 21 to expand. The pin 19 corresponds to the stopper in the form of a short pin, which is disclosed in the above-mentioned JP-A-2003-157122 and constitutes the expanding means. In the pivotable arm 14, the slot 15 is formed to construct the linkage with which an unillustrated extension arm is arranged in continuation.
FIG. 16 is now referred to. In the conventional art disclosed in JP-A-2003-157122 and the like, a point a on a circumferential sidewall of the arm portion 21a of the torsion coil spring 21 and a point b on a side edge of the arm portion 21a of the torsion coil spring 21 are in contact with each other in the neutral position. By a pivotal movement of the pivotable arm 14 over an angle of θ2 as a result of pivotal control of the unillustrated control lever, for example, in the predetermined direction, however, the point of contact of the torsion coil spring 21 with the pin 19 arranged on the pivotable arm 14 shifts from the above-mentioned point b to a point c. Namely, as a result of repeated pivotal control of the control lever, the sliding contact between the pin 19 on the pivotable arm 14 and the arm portion 21a of the torsion coil spring 21 is repeated, and as a result, abrasion tends to occur at their sliding parts.
When such abrasion occurs, a recessed portion formed on the arm portion 21a of the torsion coil spring 21 by the abrasion enters another recessed portion formed on the circumferential sidewall of the pin 19 by the abrasion, thereby developing a situation that the pivotable arm 14 shown in FIG. 17A fails to return fully to the original neutral position, to which the pivotable arm 14 is supposed to return, and stops at a position nearer by an angle η than the neutral position.
When there occurs the situation that the pivotable arm 14 fails by the angle η to fully return to the neutral position as mentioned above, the output voltage from the rotary potentiometer 11 becomes an output error ΔV as shown in the above-described FIG. 15 although it is supposed to become 0 V at the neutral position.
A similar situation takes place when the unillustrated control lever is pivotally controlled in the direction opposite to the above-mentioned direction. As illustrated in FIG. 17B, even when the control lever is controlled back to the neutral position, there arises a situation that as a result of the abrasion of the pin 19 on the pivotable arm 14 and the arm portion 21b of the torsion coil spring 21, the pivotable arm 14 fails by an angle η to fully return to the original neutral position to which the pivotable arm 14 is supposed to return.
In the conventional art equipped with a torsion coil spring, including the technique disclosed in JP-A-2003-157122, abrasion tends to occur between the arm portions 21a, 21b of the torsion coil spring 21 and the pin 19 on the pivotable arm, said pin 19 serving to expand these arm portions 21a, 21b, as a result of pivotal movements of the pivotable arm 14 of the rotary potentiometer 1 by repeated pivotal control of the control lever. The conventional art, therefore, involves the problem that, when the control lever is controlled back to the neutral position, the abrasion causes a displacement relative to the original neutral position to which the pivotable arm 14 is supposed to return and the displacement leads to deteriorations in output characteristics.